As is known in the art, many disk drive data storage systems have a plurality of interconnected enclosures. One such system, shown in FIG. 1, includes a plurality of disk drive enclosures coupled to a pair of redundant ports, port A and port B of a data storage processor through wire fibre channel cables, as shown. In general, each of the enclosures is identical in construction; an exemplary one thereof is shown in FIG. 2 to include dual ported disk drives. The disk drives are coupled to a link control card (LCC). The LCC has a pair of primary ports (PRIM) and a pair of expansion ports (EXP). The cabinets are interconnected in a daisy chain manner shown in FIG. 2 with, as noted above, wire fibre channel cables. Applications for the disk drives enclosures include, for example, JBOD (Just a Bunch Of Disks), RAID (Redundant Array of Independent Disks), and SAN (Storage Area Network).
The LCC includes a pair of diplexers coupled to the primary ports and expansion ports, as shown. Each one of the diplexers is here, for example, a diplexer such as that described in U.S. Pat. No. 5,901,151, entitled “System for orthogonal signal multiplexing”, inventor Bleiweiss, et al., issued May 4, 1999, now assigned to the same assignee as the present inventions. The diplexers are coupled to a cut through switch sections, here for example, that manufactured by PMC-Sierra, Burnaby, B.C., Canada. Thus, the disk drives are interconnected by a high-speed serial data communication path such as a Fibre Channel arbitrated loop. Each LCC includes an environmental monitor. Control signals to the environmental monitor are low frequency signals compared to the frequency signals of the signals carrying user data on the fibre channel cables. Both the low frequency and high frequency signals pass through the fibre channel cables. Thus, the fibre channel cables carry both high data rate user data that passes to and from the disk drives and low frequency signals for the environmental monitor. FIG. 3 shows the LCC in more detail. It is noted that capacitors C hare placed between the diplexers and the cut through switch section to block the low frequency signals while allowing the high data rate user data to pass to and from the disk drives.
Referring again to FIG. 1, it is noted that currently, in many systems, the electrically conductive (e.g., copper) fibre channel cables of 5 meters length between enclosures is the maximum distance a signal can travel. While optical cables offer increased distance, the connectors at the ports of the LCC are not suited for fiber optic cables. Also, fiber optic cables do not support both the high frequency data rate signals and the low frequency signals for the LCC.